1. Field of the Invention
The present invention relates in general to a method and apparatus for providing a visual indication of the difference in frequency between that of an input signal or waveform and a reference frequency. Although not limited thereto, the invention is particularly suited for use as a strobe tuning aid wherein the difference in pitch between a detected musical note and a reference frequency can be visually indicated.
2. Description of the Background Art
U.S. Pat. No. 3,901,120 by Youngquist and U.S. Pat. No. 5,777,248 by Campbell, among others, describe dynamic fundamental frequency (musical xe2x80x9cpitchxe2x80x9d) comparison systems that respond in essentially instantaneous ways to electrical or acoustic input. However, they are limited in the relatively discrete and physically large visual elements required in their implementations. Thus, when the process inherent to these systems requires a change as to which elements are to be activated (i.e., pattern xe2x80x9cmovementxe2x80x9d), there is necessarily either a delay introduced (during such time as the process yields intermediate values of phase in lit and extinguished visual elements) or a period of visually noticeable blurring in which adjacent visual elements are lit at less than full duration (and/or intensity) in proportion to the intermediate phases of frequency differences between the xe2x80x9creference frequencyxe2x80x9d and the input xe2x80x9cpitchxe2x80x9d. Since the human eye is not nearly as discerning in evaluating intensity variations in said visual elements as it is in detecting slight movement of highly contrasting visual boundaries, such prior systems are not particularly effective in representing small discrepancies between reference frequency and input xe2x80x9cpitchxe2x80x9d. Said delays or difficulties in evaluating pattern xe2x80x9cmovementxe2x80x9d lead to various frustrations for users such as limiting the effective resolution of the devices and increasing the undesirable tendency to xe2x80x9cover-shootxe2x80x9d the target reference frequency when adjusting the input xe2x80x9cpitchxe2x80x9d.
Similarly, U.S. Pat. No. 4,457,203 by Schoenberg, et al. and U.S. Pat. No. 4,589,324 by Aronstein disclose dynamic displays for automatic sound signal analyzing equipment that display the closest recognized musical note to that being played or sung by a musician, whether the note is sharp or flat or in tune and if sharp or flat, the extent to which it is sharp or flat by means of a strobe-like xe2x80x9cmovingxe2x80x9d bar pattern. The rate of change of the xe2x80x9cmovingxe2x80x9d bar pattern occurs as a result of an analysis of the input xe2x80x9cpitchxe2x80x9d or xe2x80x9cfundamental periodxe2x80x9d, and thus requires a certain amount of time to perform the analysis before the bar pattern can be altered in response to said input xe2x80x9cpitchxe2x80x9d. Moreover, in a similar manner to Youngquist and Campbell, the image elementsxe2x80x94in this case, rectangular barsxe2x80x94are relatively large, discrete areas which are sequenced. Consequently, such an implementation also suffers from the same indeterminacy in reading small discrepancies between the reference frequency and input xe2x80x9cpitchxe2x80x9dxe2x80x94the very condition under which the user most needs precise and instantaneous visual indication from such a device.
The present invention employs an improved technique to indicate the relative xe2x80x9cpitchxe2x80x9d of an input that is more responsive than the techniques described in the prior art. The primary differentiating factor between the present invention and the devices described by Schoenberg, et al and by Aronstein is that the rate of change in the displayed image pattern in the subject system is not a result of any analytical calculation, interpolation, or average of the input xe2x80x9cfundamental periodxe2x80x9d or xe2x80x9cpitchxe2x80x9d as it is in the aforementioned prior art (and typical of musical tuners in general). Instead it is the consequence of an always immediate display of an image pattern whose position is determined by a calculation based upon a reference frequency. The advantage is an image that is smoothly varying and nearly instantaneously responsive to a particular phase or portion of the xe2x80x9cfundamental periodxe2x80x9d segments of the input waveform (to the limit of the underlying electronic circuit speed). This response is orders of magnitude faster than the plurality of input xe2x80x9cfundamental periodxe2x80x9d segments or intervals required for the calculations that limit the responsiveness in tuning concepts like that of Schoenberg, et al. and Aronstein.
The present invention differs from and represents an improvement upon Youngquist and others by using reference frequency timing to determine the position of an image pattern on a visual display as opposed to using the relative phase of a reference frequency signal to determine, in part, the actuation of individual light elements (e.g., pixels) to sequentially form an image from discrete elements.
The effect of this improved method is similar to that of a desirable, true stroboscopic effect (such as that described in U.S. Pat. No. 5,877,443 by Arends, et al.) but does not require any expensive and wear-prone mechanically moving elements.
In its broadest sense, the invention comprises a method and apparatus for carrying out the same wherein a first, reference frequency and a second frequency of an input waveform are employed to control a visual display so that one or more image patterns are generated on the display in such a manner that one or more image objects within the patterns appear to move in a direction and at a rate that is indicative of the magnitude and sign of a difference in said frequencies. The reference frequency is employed to determine the position or location on the display at any instant of time where the image patterns or objects are to be generated. More particularly, the reference frequency determines the rate of movement or displacement of the pattern along one or more axes of the display. The second frequency of the input waveform is employed to determine the discrete time periods at which the image patterns or object will be visible. More particularly, a processor or other circuit detects when a unique portion of each of a sequence of fundamental period segments in the input waveform occurs and selectively renders the image patterns visible on the display in response thereto. Thus, each time the unique portion of the fundamental period segment is detected, or after a plurality of such occurrences, the processor or circuit renders visible the image pattern on the visual display at that time and at a position that is dependent on the first frequency. As a result, the image pattern appears to move across the visual display in a direction and at a rate that is dependent on the sign and the magnitude of the difference between the first and second frequency.
Preferably, the first frequency is a known reference that can be selected as desired. The second frequency is preferably that of an external input signal or waveform, whose frequency is to be determined relative to the reference frequency. In a musical strobe tuner application, the reference frequency is generated or represented by an internal electrical signal or software construct that typically corresponds to a reference musical note, and the external input signal or waveform is an electrical signal or waveform that corresponds to a musical note from a musical instrument, that is to be tuned to the reference musical note. It should be understood, however, that the invention could be used to determine the difference between frequencies in any form.